1. Field of the Invention
The present invention relates to a slave and node, and a processing unit and a network power supply monitor system, and an input/output device power supply monitoring system.
2. Related Art
As well known, in factory automation (hereafter referred to as “FA”), an I/O device is connected to a programmable controller (hereafter referred to as “PLC”) directly or via a network. A PLC is designed to control overall FA system by obtaining as Input data Information from such input devices as a switch or sensor that are a sort of the associated I/O devices, executing, in accordance with a pre-installed user program, an arithmetic operation with the associated input data obtained, to determine content of control to an output device that is a sort of the I/O device, and outputting control data corresponding to the control content, to such output devices as a valve or actuator, motor, etc.
More specifically, control in a CPU unit of PLC incorporates into an I/O memory of CPU unit a signal entered from an input device connected to an input unit (IN refresh), performs a logical operation (execution of an operation) based on a user program organized in a pre-registered ladder language, writes into the I/O memory execution result of that operation and sending it out to an output unit (OUT refresh), thereby the output unit performing a control of driving or stopping the output device, and subsequently executes so-called peripheral operations, such as processing of communications through a communication network. Thus, PLC processes IN refresh, execution of an operation, OUT refresh, and peripheral processing cyclically and repeatedly.
Such a PLC is comprised of a plurality of units. In other words, it is comprised of various units such an a power supply unit of a power supply source, a CPU unit that supervises control of the entire PLC, an input unit that inputs a signal of a switch or sensor attached to a suitable place of the production apparatus or equipment of FA, an output unit that outputs control output to an actuator, etc., an input/output device that combines input with output, a communications unit to connect with a communication network, etc.
In addition, a network system called a remote I/O is known. In this system, a master is connected to PLC unit to which a slave is connected via DeviceNet (registered trademark), etc.
Though this slave is IN slave that incorporates an input signal, OUT slave that outputs an output signal, Mix slave that inputs and outputs, etc., It shall be herein referred to as a slave. And, various devices of a sensor or relay are connected to terminals of the slave. In addition, as mentioned above, a master unit is one of the units that constitute PLC and is incorporated into PLC. With this, sensing information that has been detected by an input device (e.g., a switch or sensor, etc.) connected to the slave will be serially communicated to the master unit via a field network, and thus incorporated into PLC. And on the side of PLC, a user program is executed based on the obtained sensing information, result of its execution is conveyed to a slave via a network, which is to send a control instruction to output devices (e.g., a relay or valve, actuator, etc.) that should operate.
In addition, reception and transmission of I/O information such as an input or output signal of a device connected to the slave are performed with communication timing that has been set in advance between the slave and master unit, are asynchronous with cyclic operations of PLC, and thus operate with different timing. And the CPU unit and master unit of PLC are connected through a bus, and thus data is sent to and received from a master unit in IN refresh or OUT refresh (I/O refresh) or peripheral service processing, among cycling processing in the CPU unit. This enables the CPU unit of PLC to connect an input or output device located remotely to a slave, and send and receive data via a network.
Incidentally, in a recent network system, demands have been growing for supervising or monitoring, as appropriate, non-limiting Information such as so-called service information or system status information, maintenance information, etc., in addition to managing and monitoring current content of control. In a traditional network system, as Input data and output data including remote I/O exist in a memory of PLC, all service information used to be obtained by organizing a program on the PLC side. For example, it can be determined by measuring operation time of devices connected to the slave or time needed for I/O information to change to a different state. In order to do the associated operation, a user will create a user program to do the measurement, and execute and process the program in the CPU unit of PLC.
However, when an attempt is made to obtain service information on the PLC side, as mentioned above, two problems will arise. Firstly, load of execution and processing of a program of PLC will increase. This is because load to execute a program to get information of the service system will be generated. Secondly, communications load between a master and slave will increase. As this requires that the latest information be always obtained from the slave, a need to communicate basic data concerning service information will arise, in addition to control information as I/O data, in communications processing between the master and slave of PLC. Thus, volume of information to be communicated will expand, and cause to increase time to process communications, and a communications cycle between the master and slave will be long.
Hence, the objective of the present invention is to reduce effects on the control system on the PLC side if information of the service system is obtained, More specifically, It alms not only to reduce control load on the PLC side compared with the prior art, but also to improve convenience of a monitor, by securing non-limiting data such as service information by the slave, measuring physical quantities (time, voltage, number of times, etc.) at the slave, and making it possible to monitor that result via a network.
Next, while illustrating a more specific network system by means of figures, we will provide supplementary descriptions on additional objectives. As shown in FIG. 1. not only PLC unit 1 and master unit 2 equipped with communications capability are integrated, but also the master unit 2 is connected with a field network 3 for sending and receiving data of the control system. Also, to this field network 3, a plurality of slaves 4a, 4b and 4c are connected.
And, to each slave 4a, 4b and 4c are connected input device 5a such as a sensor, etc., and output device 5b such as a valve, motor, etc. In addition, in the shown example, slave 4a is also called IN slave as only input device 5a is connected to it, slave 4b is also called OUT slave as only output device 5b is connected to it, and slave 4c is also called Mix slave as input device 5a and output device 5b are connected to it. Note that in the following description, if no distinction needs to be made, in particular, they are simply referred to as a slave and also given a sign “4”. In addition, if input device 5a does not need to be distinguished from output device 5b, they are simply called a device and also given a sign “5”.
In the network system of the associated configuration, a network power supply apparatus 6 is placed from which power source Is supplied to a plurality of slaves 4 via a field network 3. And, power source may also be supplied, via slave 4, to devices 5 connected to each slave 4, using the power source supplied from the above-mentioned network power supply apparatus 6 to the slave 4.
In addition, a power supply source to various devices 5 is not limited to the above-mentioned network power supply apparatus 6, and, for instance, an Input/output device power supply apparatus 7 that is separately provided may be used. In other words, power supply output of the input/output device power supply apparatus 7 is given to each slave 4 through which power source is supplied to the devices 5. Note here that the input/output power supply apparatus 7 is a power source only for the devices 5 and thus power source is supplied to the slave 4 from the network power supply apparatus 6.
Incidentally, when supply of power source from the above-mentioned network power supply apparatus 6 to each slave 4 is considered, voltage will drop at the field network 3 because a resistance value of cables comprising the associated network is not zero though power source is supplied to each slave 4 through the field network 3. For this reason, voltage actually applied to the slave 4 drops from output voltage at the network power supply source 6. Therefore, voltage drop will increase to the slave 4 that is remote from the network power supply apparatus 6, and thus correct supply voltage that can satisfy provisions may not be obtained at a transmission/reception circuit chip in the slave 4 or MPU of the slave, etc.
Now, in order to normally operate this system, although a limit can be placed on the length of cables to be used in the field network 3, for instance, it is impossible to decide the cable length assuming a voltage drop which results from turning ON of devices 5 connected to the slave 4, etc. In addition, if the cable length is determined with a sufficient margin included, wiring may not be possible due to insufficient length of cables at a site where FA system is to be constructed.
Now, in order to normally operate this FA system, it is necessary not only to actually construct a system on a site, but also to ensure that source voltage to be supplied to each slave 4 is proper voltage that can satisfy the standard. However, it was the only way to ensure that this supply voltage is at a proper level is that a worker goes to a site and directly measures supply voltage of each slave by using a voltmeter, etc. Therefore, the associated work is not only very time-consuming but also complicated because a slave is sometimes installed on a back of the apparatus which is not easy to measure, etc.
In addition, there was no means of monitoring a voltage value of supply voltage at each slave. This sometimes led to inconvenience that abnormal conditions could only be detected when communications with the slave is disabled due to voltage drop in operation.
Furthermore, if a power supply source of the device 5 is the Input/output device power supply apparatus 7, a problem similar to those mentioned above will occur. In other words, there was the problem that PLC 1 or the master unit 2, which are a host, as well as a monitoring unit or configurator, to be discussed later, cannot know state of power supply of the input/output device power supply apparatus 7. The following problems also occurred in the master unit 2 and thus in PLC unit 1, which are a host.
If bit data corresponding to an input signal from the input device 5a connected to the said slave 4 that was received from the slave 4 via field network 3 was 0, a determination could not be made on whether the input signal was 0 because the said input device 5a actually turned OFF, or the input signal was 0 as a neutral operation because there was no supply voltage to the input device 5a, thereby disabling the device itself.
If bit data corresponding to an output signal to the output device 5b that was sent to the slave 4 via field network 4 was 0, a determination could not be made on whether the output device 5b has stopped because the output signal to the associated output device 5b actually turned OFF and thus 0 data was output, or the output device 5b itself is disabled because there was no supply voltage to the output device 5b. For this reason, there was a problem that reliability of the system was degraded.
In addition, to solve the problems described above, by judging whether or not there is a response from the slave 4 when a message is regularly sent to the slave 4 from the master unit 2 and PLC unit 1, for instance, it can be decided if the device receives normal voltage supply or not. To carry out associated operation, however, PLC should make judgment on transmission of a message and reception of a response, which will cause a problem that inherent control of the device 5 will be affected. Thus, the present invention is intended to reduce effects on the control system on the PLC side when supply voltage on the slave side of the remote I/O is obtained as service information.
On the other hand, FIG. 2 shows another specific system configuration. In other words, not only PLC unit 1 and master unit 2 with the communications capability are integrated, but also that master unit 2 is connected to the field network 3. OUT slave 4b or IN slave 4a is also connected to this field network 3. Associated basic network configuration is similar to that shown in FIG. 1.
And, in this example, the actuator 8 is connected to OUT slave 4b as output device 5b. In this actuator 8, upon receipt of a control instruction (ON signal) from PLC unit 1, OUT slave 4b turns ON the I/O terminal (OUT terminal) to which the actuator 8 is connected, whereupon the mobile unit 8a will move forward.
On the other hand, the sensor 9 is connected to IN slave 4a as input device 5a, and this sensor 9 monitors operation of the actuator 8. In other words, when the mobile unit 8a in the actuator 8 moves to a predetermined position (a position indicated by a dotted line in the figure), the sensor detects the mobile unit 8a, outputting a detection signal.
As that detection signal is provided to IN slave 4a, IN slave 4A outputs to PLC unit 1 a notice that it received the detection signal (i.e., predetermined I/O terminal (IN terminal) turned ON: operation complete notice). As PLC unit knows from this that the actuator 8 has moved for predetermined volume, it will send an instruction to stop (instruction to return to the origin) to OUT slave 4.
Now to actually perform the operation described above, each slave 4a and 4b performs master-to-slave communications with the master unit 2, and transmits and receives each signal (data) described above. Therefore, PLC unit I will communicate with each slave 4a and 4b via associated master unit 2.
In addition, PLC unit 1 cyclically performs operations according to a user program, wherein IN/OUT refresh operations are executed in every one cycle. Then, it sends a signal to OUT slave 4b or receives a signal from IN slave 4a. On the other hand, in the master-to-slave communications, asynchronous with cyclic operations on the PLC unit 1 side discussed above, carries out communications with predetermined slaves with a certain timing (communications cycle).
Incidentally, there is a demand for monitoring of operating time of the actuator 8, namely, period during which the mobile unit 8a Is moving. This is because a comparison between operating time and standard time, for example, can be used in determining if the actuator 8 is normally operating or not or in estimating service life due to deterioration in action of the actuator. However, traditionally, PLC unit side 1 should measure time based on ON/OFF information obtained from the slave 4a and 4b, and thus generate a program for monitoring, incorporate it into the user program, and execute it. In other words, the timer is started when PLC unit 1 outputs the instruction to operate (ON signal) to OUT slave 4b, and stopped when ON signal of IN terminal from IN slave 4a (operation complete notice) is received. With this, a value of the timer is obtained, and thus operating time will be known.
However, in the associated method, in order to obtain operating time information as service information, a need to execute the operation to measure operating time will arise, in addition to the inherent operation to control devices on the PLC side. Also, this applies to monitoring of the operating time of the input devices as well. In other words, if there are two input devices (sensors) that monitor a state of an apparatus, judgment can be made on whether the apparatus is normally operating or not, by monitoring time (operating time) from when one sensor detects the apparatus enters into one condition, till other sensor can detect the said apparatus is in another condition, etc.
However, execution of additional operations to determine the operating time described above while operations are cyclically processed on PLC unit 1 side for controlling the entire FA system will hamper high-speed control. Moreover, another problem will be caused wherein as the number of devices to be processed grows, additional operations on the PLC side will increase because more operations will be needed to calculate the operating time on the PLC side. In other words, as described above, the operating time will be determined by cyclically performing operations at PLC unit 1 every time, thereby leading to execution of wasteful operations.